Corn steep liquor is the first by-product of the corn wet-milling process. In that process shelled, air-cleaned corn is soaked or steeped at a temperature of 45.degree.-50.degree. C. for 30 to 48 hours in water initially containing about 0.1 to 0.2% sulfur dioxide. During the steeping or soaking process soluble components of the corn are dissolved in the steeping liquid, and the corn is softened thus facilitating the subsequent grinding process. The steeping liquid, sometimes called light steep water, is separated from the softened corn and concentrated by evaporation to a solids content of about 50%; the resulting concentrate is known in the art as "heavy steep water" or more commonly as "corn steep liquor," sometimes referred to herein as "CSL". It contains dissolved minerals, carbohydrates, and corn proteins, as well as organic acids (particularly lactic acid) and modified corn proteins (amino acids and polypeptides) which result from the enzymatic activity associated with the one or more natural fermentations which take place during the corn steeping process. The composition of corn steep liquor varies with the type of corn, pH of the steeping liquid (usually 3.8-4.5), the content of the water used in the steeping process (it is often recycled from other steps of the corn-wet-milling process), and steeping time and temperature. Depending on the steeping conditions, which can vary greatly from time to time in any given plant, corn steep liquor can have significant variations in relative concentrations of corn extracts and fermentation products of corn extracts, which compositional variations can have marked effects on the physical characteristics of individual lots of corn steep liquor.
Corn steep liquor finds a wide variety of uses. Primarily it is utilized either alone or in combination with other products or by-products of the corn-wet-milling process as a binder and a valuable nutritive component of animal feeds and as a nutrient medium for commercial fermentations (particularly for antibiotic production).
An industry-wide problem associated with the production and handling of corn steep liquor and liquid CSL-containing compositions is the tendency of some lots of CSL or "liver" or gel in the CSL evaporators as well as in storage, mixing, and transport tanks. When this condition occurs, the CSL or CSL-containing liquid composition is difficult, if not impossible, to pump or otherwise handle. This results in loss of employee time and loss of facilities and equipment use for both the CSL producer and CSL product customers. In instances where the livered CSL has gelled, sometimes to almost a rubber-like consistency, the only practical solution to the problem is the manual/mechanical disposal or removal of the gel.
Several solutions to the "livering" and related "scaling" problems which periodically attend the evaporation of light steep water and the storage and transport of corn steep liquor and liquid CSL-containing compositions have been proposed in the art. U.S. Pat. 2,515,157, issued Dec. 8, 1945 describes and claims a treatment of corn steep water with a source of aluminum ions which serves as a precipitant for the naturally occurring phytate in the corn steep water. Precipitation of the phytates as the insoluble aluminum salts in accordance with the described process is said to provide a concentrated liquid nutrient for penicillin-producing molds which does not deposit an objectionable sludge during shipment or storage.
U.S. Pat. No. 1,918,812 likewise acknowledges that "the boiling of the steep water is attended by an objectionable fouling and scaling of the interior of the evaporators. Apparently two kinds of scale are formed. One is called `rubber` scale and consists largely of protein material, with which other materials in suspension may be aggregated. The other is called `hard` scale and consists largely of mineral salts. Actually the deposits may be made up of both types of scale in intimate mixture . . . " That patent discloses that the problem can be overcome by heating the steep water before evaporation to a temperature between 95.degree. and 140.degree. F. until the scale forming substances are converted to naturally occurring biochemical activity into non-scale forming substances and thereafter evaporating the steep water.
U.S. Pat. No. 2,298,623 describes a method for reducing scale forming tendencies of concentrated corn steep water which method comprises heating the steep water prior to concentration under pressure to temperatures ranging between 225.degree. F. and 300.degree. F.